The structure of GP zones in Cu-10.9 at.% Be

Abstract

For a series of aging treatments at 538 K of a single crystal of Cu-10.9 at.% Be, the absolute diffuse X-ray intensity was measured with a wavelength of 1.4 Å, in a volume in reciprocal space sufficient to separate the contributions from clustering and those from atomic displacements. The zones are a mixture of Be-rich single and multilayered {100} planes. As aging proceeds, the zones increase in thickness and diameter. The nearest Cu planes collapse toward the zones, but subsequent planes are further away than the average interplanar distance. These displacements fall to zero 5–7 layers into the matrix. The {110} 〈11̄0〉 shear strain in the zones is ~0.05. The stair-step arrangement of these regions reported previously is supported, and this is inherited from the 〈11̄0〉 alignment of the ellipsoidal clusters present in the as-quenched condition. The γ″ phase, which appears in addition to GP zones for long aging times, is a monoclinic ordered Cu-Be array which arises from a distortion of four b.c.t. cells in the f.c.c. matrix. The shear strain in this phase is ~0.08 on the {110} 〈11̄0〉 system.